Status and name
Astrophytum myriostigma subsp. quadricostatum (H.Moeller) K.Kayser is accepted in POWO. Its synonyms include names associated with tamaulipense. The 2019 paper supports priority of the epithet quadricostatum for Jaumave valley populations in Tamaulipas. [2-WWW] [Montanucci and Kleszewski 2019]
Identification and variation
The epithet means four-ribbed, but populations contain plants with different rib numbers. In Jaumave, 25% of 28 plants had four ribs and 75% five. In San Antonio, only 6.2% of 65 individuals had four ribs. Plants with four to seven ribs were recorded in Los Ébanos. Rib number is descriptive but insufficient alone to identify the subspecies. [Montanucci and Kleszewski 2019]
The 2019 description gives adults about 48–50 cm tall and up to 25 cm in diameter. Four or five ribs are most common, with more less frequent. Seedlings can produce dark, curved spines 1–4 mm long, which disappear during further development. Hairs may be dense, sparse or very few, depending on population. [Montanucci and Kleszewski 2019]
Flowers, fruits and seeds
Flowers are yellow with one to three tepal rows. The redescription gave a diameter of 26–60 mm. In comparative series, Jaumave and San Antonio flowers were smaller on average than those of the nominate subspecies sample. Fruit and seed data supplement identification and show population differences. [Montanucci and Kleszewski 2019]
Range and cultivation
The subspecies is associated with Tamaulipas. In the atlas, cultivated four-ribbed plants without provenance data remain identified as four-ribbed A. myriostigma. This also applies to Onzuka quadricostatum. Similar appearance in cultivated selections does not document origin in the Jaumave valley. [2-WWW] [Montanucci and Kleszewski 2019] [11-WWW]
Cultivation follows A. myriostigma principles. In propagation, records of seed and parent provenance are more valuable than selection for rib number alone. Growth may change rib number, and offspring may retain broader variation than the pair selected for pollination. [Szychowski b.d.a] [Montanucci and Kleszewski 2019]